Then are many electronic applications for which data needs to be transmitted at high speeds over hand-limited channels. For example, data storage systems, servers, data communication systems, and digital media systems all need to provide high-speed serial links over band-limited channels. This can be accomplished by providing a transmitter at one end and a receiver at the other end of a “telecommunications channel” or “communication link” and sending or receiving signals over the channel using a communication interface.
Digital communication interfaces are used in a number of applications for electronic devices, and include standard communication specifications such as Universal Serial Bus (USB), Serial Advanced Technology Attachment (SATA), Firewire, etc. USB, for example, is a commonly-used device interface standard that allows data communication between a host and one or more peripheral devices. USB 3.0, for example, provides greater bandwidth over previous versions of that interface and full-duplex communication. However, the high-speed data signals used in more recent standards such as USB 3.0 may also introduce noise and jitter due to signal attenuation, causing undesirable signal voltage swing and degraded signal quality.
One way to reduce signal quality degradation is to use redrivers and/or repeaters in a communication system. A redriver receives a transmitted signal and conditions it to reduce the effects of noise, crosstalk, inter-symbol interference (ISI), and other undesirable signal degradation from transmission, and then sends the conditioned signal to the receiver over a communication link. Redrivers can allow the use of extended transmission channels that have lengths larger than allowed by the requirements of the communication specification, including longer circuit board traces and/or longer transmission cables.
One way that redrivers and other transmission devices can condition signals for transmission is by applying “emphasis” to the signal to be transmitted, including pre-emphasis and/or de-emphasis. The signal-to-noise ratio (SNR) of the transmitted signal can be improved by increasing or decreasing the magnitude of particular frequencies in the signal. For example, in some data transmission implementations, noise occurring in the transmission channel can reduce the amplitude of higher-frequency components of a transmitted signal, especially in channels of longer length. De-emphasis can be used at the transmitter to reduce the amplitude of lower-frequency components of the signal so as to achieve uniform amplitude of all components of the signal at the receiver, thus reducing the effects of noise on the transmitted signal. However, emphasis techniques may cause undesired effects for signals in some transmission applications.
These and other limitations of the prior art will become apparent to those of skill in the art upon a reading of the following descriptions and a study of the several figures of the drawing.